1. Field of the Invention
The invention is in the field of glass manufacture, and particularly relates to the manufacture of non-oxide glasses of a type described as halide glasses. Specifically, the invention relates to novel metal fluoride glass compositions which are of interest for glass products such as infrared-transparent optical devices, e.g. glass optical waveguides.
2. Description of the Prior Art
Among the best known of the halide glass-forming systems are the compositions based on BeF.sub.2. However, these compositions share the shortcomings of most other halide glasses in that they exhibit relatively short working ranges and are prone to devitrification. In addition, BeF.sub.2 is both hygroscopic and highly toxic.
A number of other fluoride glass compositions have been recently discovered. U.S. Pat. No. 4,141,741 discloses a family of ZrF.sub.4 -based glass-forming compositions in the ZrF.sub.4 -BaF.sub.2 -ThF.sub.4 composition system which exhibit infrared transparency out to about 7 microns and which are non-hygroscopic. U.S. Pat. No. 4,308,066 discloses a family of fluoride compositions based on ZrF.sub.4 and/or AlF.sub.3, containing 20-80 mole percent of CaF.sub.2, SrF.sub.2, BaF.sub.2 and/or PbF.sub.2, which will form glasses if rapidly quenched.
M. Matecki et al. describe, in Mat. Res. Bull., 17, 1035-1043 (1982), a series of ThF.sub.4 -ZrF.sub.4 compositions containing fluorides selected from the group LaF.sub.3, YF.sub.3, CdF.sub.3, LuF.sub.3, ScF.sub.3 as glass modifiers. These compositions provide relatively stable glasses, exhibiting glass transition temperatures in the 460.degree.-515.degree. C. range, which can be formed by casting and are infrared-transparent out to about 7 microns.
Glasses based on fluorides other than ZrF.sub.4 are also known. S. Shibata et al. disclose, in Mat. Res. Bull., 15, 129-137 (1980), a family of PbF.sub.2 -based glasses in the PbF.sub.2 -AlF.sub.3 system which will form glasses if rapidly quenched. M. Matecki et al., Mat. Res. Bull., 17, 1275-1281 (1982) report glasses based on CdF.sub.2, including binary CdF.sub.2 -BaF.sub.2 and ternary CdF.sub.2 -BaF.sub.2 -ZnF.sub.2 compositions optionally containing AlF.sub.3, YbF.sub.3, ThF.sub.4 and/or alkali metal fluorides. These compositions will also form thin, infrared transmitting glass elements if rapidly quenched.